1. Field of the Invention
The present invention relates to a turbomolecular pump that generates vacuum in a vacuum chamber or the like.
2. Description of the Related Art
Conventionally, the manufacture of IC products and the like involves performing each process in a respective operation chamber, such that once a process is over in one operation chamber, the product being processed is transferred to a subsequent operation chamber. Turbomolecular pumps have come to be used herein when, for instance, vacuum must be created in the interior of one such operation chamber (vacuum chamber).
For example, a composite-type turbomolecular pump such as the one illustrated in FIG. 4 is one instance of such turbomolecular pumps. In the figure, a suction port portion 102 and a discharge port portion 103 are formed in a casing 101. A rotor 104 is housed in the casing 101. Rotor blades 105 that extend towards the inner peripheral wall face of the casing 101, and a cylindrical rotor cylinder portion 117 are formed in the rotor 104.
Stator blades 106 that correspond respectively to the rotor blades 105 are attached to the stator side. A stator thread groove 115a is attached to the rotor cylinder portion 117, on the outer side of the rotor cylinder portion 117, and a stator thread groove 115b is attached to the inner side of the rotor cylinder portion 117. An evacuation mechanism that relies thus on thread grooves is referred to as a Holweck-type mechanism.
The gas that is sucked through the suction port portion 102 is compressed as a result of the interaction between the rotor blades 105 and the stator blades 106 that rotate at high speed, is further compressed by the rotor cylinder portion 117 and the stator thread grooves 115a, 115b, and is discharged out of the discharge port portion 103.
An opening 151 is provided at a portion at which the rotor cylinder portion 117 projects in the radial direction of the rotating shaft, in order to lead gas towards a flow channel inside the rotor cylinder portion 117.
In this conventional example, thus, pumping capacity is enhanced through evacuation by using inner and outer Holweck portions of the rotor cylinder portion 117. A specific example of a turbomolecular pump of such type is disclosed in Japanese Unexamined Utility Model Application Publication No. H5-38389.
A groove 161 for arranging therein a resin for a balancer is formed at the inner lower portion of the rotor cylinder portion 117.
That is because the center of gravity of the rotor 104 is located at the top; accordingly, the balancer is disposed in the inner lower portion, at a site as distant as possible from the center of gravity, so as to significantly bring out the effect of the balancer.